361 research outputs found
One-dimensional in-plane edge domain walls in ultrathin ferromagnetic films
We study existence and properties of one-dimensional edge domain walls in
ultrathin ferromagnetic films with uniaxial in-plane magnetic anisotropy. In
these materials, the magnetization vector is constrained to lie entirely in the
film plane, with the preferred directions dictated by the magnetocrystalline
easy axis. We consider magnetization profiles in the vicinity of a straight
film edge oriented at an arbitrary angle with respect to the easy axis. To
minimize the micromagnetic energy, these profiles form transition layers in
which the magnetization vector rotates away from the direction of the easy axis
to align with the film edge. We prove existence of edge domain walls as
minimizers of the appropriate one-dimensional micromagnetic energy functional
and show that they are classical solutions of the associated Euler-Lagrange
equation with Dirichlet boundary condition at the edge. We also perform a
numerical study of these one-dimensional domain walls and uncover further
properties of these domain wall profiles
Instabilities and disorder of the domain patterns in the systems with competing interactions
The dynamics of the domains is studied in a two-dimensional model of the
microphase separation of diblock copolymers in the vicinity of the transition.
A criterion for the validity of the mean field theory is derived. It is shown
that at certain temperatures the ordered hexagonal pattern becomes unstable
with respect to the two types of instabilities: the radially-nonsymmetric
distortions of the domains and the repumping of the order parameter between the
neighbors. Both these instabilities may lead to the transformation of the
regular hexagonal pattern into a disordered pattern.Comment: ReVTeX, 4 pages, 3 figures (postscript); submitted to Phys. Rev. Let
Structure and properties of nanostructured ZrN coatings obtained by vacuum-arc evaporation using RF discharge
Nanostructured films of zirconium nitride have been synthesized using an ion plasma vacuum-arc deposition technique in combination with a high-frequency (RF) discharge on AISI 430 stainless steel at 150 °C. Structural examination using X-ray fluorescence (XRF), X-ray diffraction (XRD), scanning electron microscopy (SEM)
with microanalysis (EDX), transmission electron microscopy (TEM), and nanoidentation was undertaken to reveal phase and chemical composition, surface morphology, microstructure and nanohardness of the coatings. The developed technology provided low-temperature film synthesis, minimized discharge breakdown decreasing formation of macroparticles (MPs) and allowed to deposit ZrN coatings with hardness variation 26.6–31.5 GPa and enhanced corrosion resistance characteristics. It was revealed that ZrN single-phase coatings of cubic modification with fine-crystalline grains of 20 nm in size were formed. The corrosion resistance of coatings has been tested in 0.9% quasiphysiological NaCl solution
Structure and properties of nanostructured ZrN coatings obtained by vacuum-arc evaporation using RF discharge
Nanostructured films of zirconium nitride have been synthesized using an ion plasma vacuum-arc deposition technique in combination with a high-frequency (RF) discharge on AISI 430 stainless steel at 150 °C. Structural examination using X-ray fluorescence (XRF), X-ray diffraction (XRD), scanning electron microscopy (SEM)
with microanalysis (EDX), transmission electron microscopy (TEM), and nanoidentation was undertaken to reveal phase and chemical composition, surface morphology, microstructure and nanohardness of the coatings. The developed technology provided low-temperature film synthesis, minimized discharge breakdown decreasing formation of macroparticles (MPs) and allowed to deposit ZrN coatings with hardness variation 26.6–31.5 GPa and enhanced corrosion resistance characteristics. It was revealed that ZrN single-phase coatings of cubic modification with fine-crystalline grains of 20 nm in size were formed. The corrosion resistance of coatings has been tested in 0.9% quasiphysiological NaCl solution
Reduced energies for thin ferromagnetic films with perpendicular anisotropy
We derive four reduced two-dimensional models that describe, at
different spatial scales, the micromagnetics of ultrathin
ferromagnetic materials of finite spatial extent featuring
perpendicular magnetic anisotropy and interfacial
Dzyaloshinskii-Moriya interaction. Starting with a microscopic model
that regularizes the stray field near the material's lateral edges,
we carry out an asymptotic analysis of the energy by means of
-convergence. Depending on the scaling assumptions on the
size of the material domain vs. the strength of dipolar interaction,
we obtain a hierarchy of the limit energies that exhibit
progressively stronger stray field effects of the material
edges. These limit energies feature, respectively, a renormalization
of the out-of-plane anisotropy, an additional local boundary penalty
term forcing out-of-plane alignment of the magnetization at the
edge, a pinned magnetization at the edge, and, finally, a pinned
magnetization and an additional field-like term that blows up at the
edge, as the sample's lateral size is increased. The pinning of the
magnetization at the edge restores the topological protection and
enables the existence of magnetic skyrmions in bounded samples.Comment: 29 pages, 1 figur
Computational assessment of environmental hazards of nitroaromatic compounds: influence of the type and position of aromatic ring substituents on toxicity
This study summarizes the results of our recent QSAR and QSPR investigations on prediction of numerous aspects of environmental behavior of nitro compounds. In this study, we applied the QSAR/QSPR models previously developed by our group for virtual screening of energetic compounds, their precursors and other compounds containing nitro groups. To make predictions on the environmental impact of nitro compounds, we analyzed the trends in the change of the experimentally obtained and QSAR/QSPR-predicted values of aqueous solubility, lipophilicity, Ames mutagenicity, bioavailability, blood–brain barrier penetration, aquatic toxicity on T. pyriformis and acute oral toxicity on rats as a function of chemical structure of nitro compounds. All the models were developed using simplex descriptors in combination with random forest (RF) modeling techniques. We interpreted the possible environmental impact (different toxicological properties) in terms of dividing considered nitro compounds based on hydrophobic and hydrophilic characteristics and in terms of the influence of their molecular fragments that promote and interfere with toxicity. In particular, we found that, in general, the presence of amide or tertiary amine groups leads to an increase in toxicity. Also, it was predicted that compounds containing a NO2 group in the para-position of a benzene ring are more toxic than meta-isomers, which, in turn, are more toxic than ortho-isomers. In general, we concluded that hydrophobic nitroaromatic compounds, especially the ones with electron-accepting substituents, halogens and amino groups, are the most environmentally hazardous
- …